Process for making composites comprising rigid-rod polymers and graphene nanoparticles

ABSTRACT

The present invention relates to composites comprising rigid-rod polymers and graphene nanoparticles, processes for the preparation thereof, nanocomposite films and fibers comprising such composites and articles containing such nanocomposite films and fibers.

This application is a divisional of U.S. application Ser. No. 13/592,327filed on Aug. 22, 2012, issued as U.S. Pat. No. 9,850,596 on Dec. 26,2017, which is expressly incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention generally relates to new polymer compositescomprising rigid-rod polymers and graphene nanoparticles and to methodsfor producing such composites.

BACKGROUND OF THE INVENTION

Graphene sheets are one-atom-thick planar sheets of sp²-bonded carbon.The strongest bond in nature, the C—C bond, covalently locks these atomsin place giving them remarkable mechanical properties. A suspendedsingle layer of graphene is one of the softest known materialscharacterized by a remarkably high Young's modulus of ˜1 TPa. See, e.g.,Bunch, J. S., at al., Nano Letters, Vol 8, No. 8, pp. 2458-2482 (2008).Theoretical and experimental results on single layer graphene nanosheetsexhibit extremely high values of elastic modulus (˜1,000 GPa), fracturestrength (˜100-400 GPa), thermal conductivity (˜5,300 Wm⁻¹ K⁻¹),mobility of charge earners (˜200,000 cm² V⁻¹ s⁻¹), large surface area(up to >2,600 m²/g), and anomalous integer and fractional quantum Halleffect. These properties make graphene very promising for manyapplications such as solar cells and hydrogen storage, batteries,supercapacitors, sensors, and nanocomposites. See Stankovich, S., etal., Nature, Vol. 442, pp. 282-286 (2008) and Kuilla, T., et al., Prog.Polym. Sci., Vol. 35. pp. 1350-1375 (2010).

To exploit the exceptional strength and conductive properties ofgraphene sheets, numerous attempts have been made to incorporategraphene sheets into polymers. However, one of the problems encounteredin making polymer-graphene composites is the difficulty in achievinggood dispersion of the graphene in the blend. As degree of graphenedispersion improves, the strength properties of the polymer compositecorrespondingly improve as well.

Layers of graphene tend to tightly agglomerate due to van der Waalsforces. Dispersing graphene is difficult because graphene agglomeratescan fall anywhere in the range of a few sheets to many hundreds ofsheets thick. In order to obtain good graphene dispersion van der Waalsforce must be overcome but conventional methods used to disperse thegraphene, such as sonication, can also damage the crystal structure ofthe sheet and, consequently, impair strength and tensile properties.Similarly, prior art methods employed to improve dispersion of graphenein a polymer matrix, in particular chemical functionalization ofgraphene, preclude high levels of loading of the graphene sheets in thepolymer composite thus compromising the strength of the compositematerial.

Accordingly, it is an object of the present invention to provide thinlayers of graphene sheets intercalated with polymer platelets to producea graphene/polymer composite having exceptional tensile strength andelongation-to-break characteristics when compared with the base polymerof the polymer composite.

SUMMARY OF THE INVENTION

The present invention relates to new polymer composites in whichgraphene nanoparticles are well-dispersed in a polymer matrix.Advantageously, the polymer composites may be provided as sheets orfibers and thus may find application as bullet-proof vests, body armor,vehicular armor, ballistic protection equipment, and as reinforcingfibers for both organic and inorganic products, such as tire cords forautomobile tires, machine belts, ceramics, polymer laminates foraircraft and other compositions requiring high strength materials.

Briefly, therefore, the present invention is directed to a polymercomposite comprising a polymer and graphene nanoparticles dispersed inthe polymer, the polymer comprising at least 50 wt % rigid rod polymerrepeat units.

Another aspect of the present invention is a polymer composite fiber,the fiber comprising a polymer and graphene nanoparticles dispersed inthe polymer, the polymer comprising at least 50 wt % rigid rod polymerrepeat units.

Another aspect of the present invention is a polymer composite film, thefilm comprising a polymer and graphene nanoparticles dispersed in thepolymer, the polymer comprising at least 50 wt % rigid rod polymerrepeat units.

Another aspect of the present invention is a process for preparing apolymer composite, the process comprising forming a reaction mixturecomprising rigid rod monomers and oligomers containing repeat unitsderived from the rigid rod monomer, the oligomers having, on average,about 5-10 repeat units, adding graphene nanoparticles to the reactionmixture, and polymerizing the reaction mixture to term a polymercomposite comprising a polymer and graphene nanoparticles dispersed tothe polymer, the polymer comprising at least 50 wt % rigid rod polymerrepeat units.

Another aspect of the present invention are articles comprising polymercomposite fiber, the fiber comprising a polymer and graphenenanoparticles dispersed in the polymer, the polymer comprising at least50 wt % rigid rod polymer repeat units.

Another aspect of the present invention are articles comprising apolymer composite in fiber or film-form, the article being selected fromthe group consisting of bullet-proof vests, body armor, vehicular armor,ballistic protection equipment, tires, machine belts, ceramics, andaircraft.

Other objects and features will be in part apparent and in part pointedout hereinafter.

Abbreviations and Definitions

The following definitions and methods are provided to better define thepresent invention and to guide those of ordinary skill in the art in thepractice of the present invention. Unless otherwise noted, terms are tobe understood according to conventional usage by those of ordinary skillin the relevant art.

When introducing elements of the present invention or the preferredembodiment(s) thereof, the articles “a,” “an,” “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising,” “including” and “having” ere intended to be inclusive andmean that there may be additional elements other than the listedelements.

Acyl: unless otherwise indicated, “acyl,” as used alone or as part ofanother group, denotes moiety formed by removal of the hydroxyl groupfrom the group —COOH of an organic carboxylic acid, e.g., RC(O)—,wherein R is R¹, R¹O—, R¹R²N—, or R¹S—, R¹ is hydrocarbyl,heterosubstituted hydrocarbyl, or heterocyclo, and R² is hydrogen,hydrocarbyl or substituted hydrocarbyl.

Aliphatic: unless otherwise indicated, “aliphatic” or “aliphatic group”means an optionally substituted, non-aromatic hydrocarbon moiety. Themoiety may be, for example, linear, branched, or cyclic mono orpolycyclic such as fused, bridging, or spiro-fused polycyclic), or acombination thereof. Unless otherwise specified, aliphatic groupscontain 1-20 carbon atoms.

Alkyl: unless otherwise indicated, the alkyl groups described herein arepreferably lower alkyl containing from one to eight carbon atoms in theprincipal chain and up to 20 carbon atoms. They may be linear, branchedor cyclic and include methyl, ethyl, propyl, butyl, hexyl and the like.

Amino: unless, otherwise indicated, the term “amino” as used hereinalone or as part of another group denotes the moiety —NR¹R² wherein R¹,and R² are independently hydrogen, hydrocarbyl substituted hydrocarbylor heterocyclo.

Amine or amino: unless otherwise indicated, the term “amine” or “amino”refers to a group of formula —N(X₈)(X₉), wherein X₈ and X₉ areindependently hydrogen, hydrocarbyl, substituted hydrocarbyl,heteroaryl, or heterocyclo, or X₈ and X₉ taken together form asubstituted or unsubstituted alicyclic, aryl, or heterocyclic moiety,each as defined in connection with such term, typically having from 3 to8 atoms in the ring, “Substituted amine,” for example, refers to a groupof formula —N(X₈)(X₉), wherein at least one of X₈ and X₉ are other thanhydrogen. “Unsubstituted amine,” for example, refers to a group offormula —N(X₈)(X₉), wherein X₈ and X₉ are both hydrogen.

Amide or Amido: unless otherwise indicated, the “amide” or “amido”moieties represent a group of the formula —CONR¹R² wherein R¹ and R² areas defined in connection with the term “amino.” “Substituted amide,” forexample, refers to a group of the formula —CONR¹R² wherein at least oneof R¹ and R² are other than hydrogen. “Unsubstituted amido,” forexample, refers to a group of the formula —CONR¹R², wherein R¹ and R²are each hydrogen.

Aryl: unless otherwise indicated, the term “aryl,” “aryl group” orsimply “Ar” refers to optionally substituted monocyclic, bicyclic, andtricyclic ring systems having a total of five to fourteen ring members,wherein at least one ring in the system is aromatic and wherein eachring in the system contains three to seven ring members. The terms“aryl,” “aryl group” or “ar” as used herein alone or as part of anothergroup denote optionally substituted homocyclic aromatic groups,preferably monocyclic or bicyclic groups containing from 6 to 12 carbonsin the ring portion, such as phenyl, biphenyl, naphthyl, substitutedphenyl, substituted biphenyl or substituted naphthyl. Phenyl andsubstituted phenyl are the more preferred aryl.

Block Copolymer: unless otherwise indicated, a “block copolymer”comprises two or more homopolymer or copolymer subunits linked bycovalent bonds. Block copolymers with two or three distinct blocks arecalled diblock copolymers and triblock copolymers, respectively. Aschematic generalization of a diblock copolymer is represented by theformula [A_(a)B_(b)C_(c) . . . ]_(m)-[X_(x)Y_(y)Z_(z) . . . ]_(n)wherein each letter stands for a constitutional or monomeric unit, andwherein each subscript to a constitutional unit represents the molefraction of that unit in the particular block, the three dots indicatethat there may be more (there may also be fewer) constitutional units ineach block and m and n indicate the molecular weight of each block inthe diblock copolymer. As suggested by the schematic, in some instances,the number and the nature of each constitutional unit is separatelycontrolled for each block. The schematic is not meant and should not beconstrued to infer any relationship whatsoever between the number ofconstitutional units or the number of different types of constitutionalunits in each of the blocks. Nor is the schematic meant to describe anyparticular number or arrangement of the constitutional units within aparticular block. In each block the constitutional units may be disposedin a purely random, an alternating random, a regular alternating, aregular block or a random block configuration unless expressly stated tobe otherwise. A purely random configuration, for example, may have thenon-limiting form: X-X-Y-Z-X-Y-Y-Z-Y-Z-Z-Z . . . . A non-limiting,exemplary alternating random configuration may have the non-limitingform: X-Y-X-Z-Y-X-Y-Z-Y-X-Z . . . , and an exemplary regular alternatingconfiguration may have the non-limiting form: X-Y-Z-X-Y-Z-X-Y-Z . . . .An exemplary regular block configuration may have the followingnon-limiting configuration: . . . X-X-X-Y-Y-Y-Z-Z-Z-X-X-X . . . , whilean exemplary random block configuration may have the non-limitingconfiguration: . . . X-X-X-Z-Z-X-X-Y-Y-Y-Y-Z-Z-Z-X-X-Z-Z-Z- . . . . Innone of the preceding generic examples is the particular juxtapositionof individual constitutional units or blocks or the number ofconstitutional units in a block or the number of blocks meant nor shouldthey be construed as in any manner bearing on or limiting the actualstructure of block copolymers forming a micelle described herein. Asused herein, the brackets enclosing the constitutional units are notmeant and are not to be construed to mean that the constitutional unitsthemselves form blocks. That is, the constitutional units within thesquare brackets may combine in any manner with the other constitutionalunits within the block, i.e., purely random, alternating random, regularalternating, regular block or random block configurations. The blockcopolymers described herein are, optionally, alternate, gradient orrandom block copolymers.

Carbocyclic: unless otherwise indicated, the term “carbocyclic” as usedherein alone or as part of another group refers to a saturated orunsaturated monocyclic or bicyclic ring in which all atoms of all ringsare carbon. Thus, the term includes cycloalkyl and aryl rings. Thecarbocyclic ring(s) may be substituted or unsubstituted. Exemplarysubstituents include one or more of the following groups: hydrocarbyl,substituted hydrocarbyl keto, hydroxy, protected hydroxy, acyl, acyloxy,alkoxy, alkenoxy, alkynoxy, aryloxy, halogen, amido, amino, nitro,cyano, thiol, ketals, acetals, esters and ethers.

Copolymer: unless otherwise indicated, “copolymer” refers to a polymerderived from two, three or more monomeric species and includesalternating copolymers, periodic copolymers, random copolymers,statistical copolymers and black copolymers.

Cyano: unless otherwise indicated, the term “cyano,” as used hereinalone or as part of another group, denotes a group of formula —CN.

Extended rod polymer repeat unit: unless otherwise indicated, “extendedrod polymer repeat unit” or “extended rod repeat unit” as used hereindescribes a repeat unit other than a rigid rod polymer repeat unit inwhich all exocyclic bonds of the aromatic/heterocyclic moieties withinthe repeat unit have a catenation angle of 180°±35°. Stated differently,the exocyclic bonds of the aromatic/heterocyclic units within a repeatunit of an extended rod polymer repeat unit have a catenation anglegreater than 180° but less than 215° or a catenation angle less than180° but greater than 145°.

Graphene: unless otherwise indicated, the term “graphene” or “graphenesheet” denotes a one-atom-thick layer of sp²-bonded carbon atoms thatare densely packed in a honeycomb crystal lattice.

Graphene nanoparticles: unless otherwise indicated, the term “graphenenanoparticles” denotes a graphene sheet or a crystalline, non-graphiticnanoparticle comprising two or more graphene sheets in a stackedarrangement.

Graphite: unless otherwise indicated, the term “graphite” denotes astructure comprised of at least 100 graphene sheets. For example, a“non-graphic” graphene nanoparticle sheet comprises fewer than 100graphene sheets.

Heteroaryl: unless otherwise indicated, the term “heteroaryl” means anaryl group wherein at least one of the ring members is a heteroatom, andpreferably 5 or 6 atoms in each ring. The heteroaromatic grouppreferably has 1 or 2 oxygen atoms, 1 or 2 sulfur atoms, and/or 1 to 4nitrogen atoms in the ring, and may be bonded to the remainder of themolecule through a carbon or heteroatom. Exemplary heteroaromaticsinclude furyl thienyl, pyridyl oxazolyl, pyrrolyl indolyl, quinolinyl,or isoquinolinyl and the like. Exemplary substituents include one ormore of the following groups: hydrocarbyl, substituted hydrocarbyl, keto(i.e., ═O), hydroxy, protected hydroxy, acyl, acyloxy, alkoxy, alkenoxy,alkynoxy, aryloxy, halogen, amido, amino, nitro, cyano, thiol, ketals,acetals, esters and ethers.

Heteroatom: unless otherwise indicated, the term “heteroatom” means anatom other than hydrogen or carbon, such as a chlorine, iodine, bromine,oxygen, sulfur, nitrogen, phosphorus, boron, arsenic, selenium orsilicon atom.

Heterocyclo: unless otherwise indicated, the terms “heterocyclo” and“heterocyclic” as used herein alone or as part of another group denoteoptionally substituted, fully saturated or unsaturated, monocyclic orbicyclic, aromatic or nonaromatic groups having at least one heteroatomin at least one ring, and preferably 5 or 6 atoms in each ring. Theheterocyclo group preferably has 1 or 2 oxygen atoms, 1 or 2 sulfuratoms, and/or 1 to 4 nitrogen atoms in the ring, and may be bonded tothe remainder of the molecule through a carbon or heteroatom. Exemplaryheterocyclo include heteroaromatics such as furyl, thienyl, pyridyl,oxazolyl, pyrrolyl, indolyl, quinolinyl, or isoquinolinyl and the like.Exemplary substituents include one or more of the following groups:hydrocarbyl, substituted hydrocarbyl, keto, hydroxy, protected hydroxy,acyl, acyloxy, alkoxy, alkenoxy, alkynoxy, aryloxy, halogen, amido,amino, nitro, cyano, thiol, ketals, acetate, esters and ethers.

Hydrocarbon: unless otherwise indicated, the terms “hydrocarbon” and“hydrocarbyl” as used herein describe organic compounds or radicalsconsisting exclusively of the elements carbon and hydrogen. Thesemoieties include alkyl, alkenyl, alkynyl and aryl moieties. Thesemoieties also include alkyl alkenyl, alkynyl, and aryl moietiessubstituted with other aliphatic or cyclic hydrocarbon groups, such asalkaryl, alkenaryl and alkynaryl. Unless otherwise indicated, thesemoieties preferably comprise 1 to 20 carbon atoms.

Non-extended/rigid rod polymer repeat unit: unless otherwise indicated,“non-extended/rigid rod polymer repeat unit” or “non-extended/rigid rodrepeat unit” as used herein describes a repeat unit that is not a rigidrod polymer repeat unit or an extended rod repeat unit.

Number Average: unless otherwise indicated, the terms “number average”or “average” as used herein in connection with the size of graphenenanoparticles means the average number of graphene sheets comprised byeach of at least 30 graphene nanoparticles in each of at least fourseparate regions of the composite, as determined by transmissionelectron microscopy (“TEM”).

Polymer: unless otherwise indicated, “polymer” includes natural andsynthetic, homopolymers and copolymers comprising multiple repeat unitsand, unless otherwise indicated, may be linear, branched, or dendritic.Examples of copolymers include, but are not limited to, randomcopolymers and block copolymers.

Rigid rod copolymer: unless otherwise indicated, “rigid rod copolymer”as used herein describes a copolymer comprising rigid rod polymer repeatunits and extended rod repeat units or non-extended/rigid rod repeatunits.

Rigid rod polymer: unless otherwise indicated, “rigid rod polymer” asused herein describes a homopolymer comprising rigid rod polymer repeatunits.

Rigid rod polymer repeat unit: unless otherwise indicated, “rigid rodpolymer repeat unit” or “rigid rod repeat unit” as used herein describesa repeat unit in which all exocyclic bonds of the aromatic/heterocyclicmoieties within the repeat unit have a catenation angle of 180°.

Substituted hydrocarbyl: unless otherwise indicated, the “substitutedhydrocarbyl” moieties described herein are hydrocarbyl moieties whichare substituted with at least one atom other than carbon, includingmoieties in which a carbon chain atom is substituted with a hetero atomsuch as nitrogen, oxygen, silicon, phosphorous, boron, sulfur, or ahalogen atom. These substituents include halogen, heterocyclo, alkoxy,alkenoxy, alkynoxy, aryloxy, hydroxy, protected hydroxy, keto, acyl,acyloxy, nitro, amino, amido, nitro, cyano, thiol, ketals, acetals,esters, ethers, and thioethers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows typical stress-strain curves for BBL and BBL/GS (80/20)fibers as more fully described in Example XVI.

FIG. 2 shows X-ray diffraction pattern of BBL and BBL/GS films as morefully described in Example XVII.

FIG. 3 shows Resonance Raman of Graphene nanoparticle, BBL and BBL/GSfilms as more fully described in Example XVI.

FIG. 4 shows weight loss in BBL/GS(80/20) fiber when heated at 20°C./minute in nitrogen as more fully described in Example XVI.

FIG. 5 is a TEM micrograph of BBL/GS (50/50) film with a layeredgraphene structure as described more fully in Example XVII.

FIG. 6 is a SEM micrograph of BBL/GS (50/50) film with a layeredgraphene structure as described more fully in Example XVII.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In general, the polymer composites of the present invention containgraphene nanoparticles that are well-dispersed in a polymer matrix. As aresult, one or more properties of the polymer composite are improvedrelative to the base polymer of the polymer composite (i.e., anotherwise identical composition but lacking the graphene nanoparticles).For example, in one embodiment the tensile strength of the polymercomposite is at least 50% greater than the tensile strength of the basepolymer of the polymer composite; in some embodiments the tensilestrength of the polymer composite is at least 60%, 100%, or even 200%greater than the tensile strength of the base polymer of the polymercomposite. By way of further example, in one embodiment theelongation-to-break characteristics of the polymer composite is at least50% greater than the tensile strength of the base polymer of the polymercomposite; in some embodiments the tensile strength of the polymercomposite is at least 100%, 200%, or even 500% greater than theelongation-to-break characteristics of the base polymer of the polymercomposite. By way of further example, in one embodiment the tensilemodulus of the composite film is at least 35%, 37%, 40%, 50% or even100% greater than the tensile modulus of the base polymer.

Graphene nanoparticles comprised by the polymer composites arecrystalline and non-graphitic. That is, the graphene nanoparticlescontain less than 100 graphene layers in a stacked arrangement. Incertain embodiments, the graphene nanoparticles comprised by the polymermatrix have, on average (number average), fewer than 75 graphene layersin a stacked arrangement. For example, in some embodiments the graphenenanoparticles comprised by the polymer matrix have, on average, fewerthan 50 graphene layers in a stacked arrangement. By way of furtherexample, the graphene nanoparticles comprised by the polymer matrixhave, on average, fewer than 40 graphene layers in a stackedarrangement. By way of further example, the graphene nanoparticlescomprised by the polymer matrix have, on average, fewer than 30 graphenelayers in a slacked arrangement. By way of further example, the graphenenanoparticles comprised by the polymer matrix have, on average, fewerthan 25 graphene layers in a stacked arrangement. By way of furtherexample, the graphene nanoparticles comprised by the polymer matrixhave, on average, fewer than 15 graphene layers in a stackedarrangement. By way of further example, the graphene nanoparticlescomprised by the polymer matrix have, on average, fewer than 10 graphenelayers in a stacked arrangement.

In general the graphene nanoparticles may comprise graphene, grapheneoxide or chemically-functionalized graphene. In a further aspect, thesuspension comprises a graphite or graphene material that has beenmodified from a starting graphite or graphene material. In one aspect,modified graphite and graphene materials include without limitation atleast one of chemically-functionalized graphene, reduced graphene,graphene, or a combination thereof. An example of reduced graphene ishighly reduced graphene. In one aspect, the graphene material can behighly reduced graphene. “Highly reduced graphene” refers to grapheneoxide that has been substantially reduced, or, for example, reduced to alevel that imparts a desired conductivity to the reduced graphene. Thus,in one aspect, the graphene material can be electrically conductive. Itis known in the art that oxygen containing functional groups, whenpresent on graphene, can interfere with electrical conductivity. Itshould be noted that it is not necessary that a reduced or highlyreduced graphene material comprise only hydrogen and carbon elements. Inone aspect, a reduced or highly reduced graphene is fully hydrogenated.In another aspect, one or more sites of a reduced or highly reducedgraphene material can comprise another element, such as for example, anitrogen or oxygen.

In a still further aspect, the graphene material can bechemically-functionalized graphene, including chemically-modifiedgraphene (CMG), which includes one-atom thick sheets of carbonoptionally functionalized with other elements. If a particular surfaceof a chemically modified graphene material, or a portion thereof, isfunctionalization, such functionalization can, in various aspects,comprise multiple functional groups and can be uniform or can varyacross any portion of the surface. For example, in one embodiment, thegraphene nanoparticles comprise sulfonated graphene sheets that aredispersible in an aqueous solution. By way of further example, thegraphene may be dispersible in acid such as phosphoric acid ormethanesulfonic acid. By way of further example, the graphene mayalternatively be functionalized with at least one nonpolar groupselected from the group consisting of alkyl groups, aryl groups, alkoxygroups, alkylaryl groups, alkoxyaryl groups, and combinations thereof.Other functional groups may be attached depending on the end use of thegraphene nanoparticles as readily understood by one skilled in the art.

The polymer composites of the present invention typically comprise atleast about 1 wt % graphene nanoparticles. For example, in oneembodiment, the polymer composite comprises at least 5 wt % graphenenanoparticles. By way of further example, in one embodiment the polymercomposite comprises at least 7.5 wt % graphene nanoparticles. By way offurther example, in one embodiment the polymer composite composes atleast 10 wt % graphene nanoparticles. By way of further example, in oneembodiment the polymer composite comprises at least 15 wt % graphenenanoparticles. In general, however, the loading of the graphenenanoparticles in the polymer composite will typically not exceed about50 wt %. For example, in one embodiment the polymer composite comprisesno more than about 40 wt % graphene nanoparticles. By way of furtherexample, in one embodiment the polymer composite comprises no more than35 wt % graphene nanoparticles. By way of further example, in oneembodiment the polymer composite comprises no more than 30 wt % graphenenanoparticles. For certain applications, the polymer composite willcontain about 5 to about 35 wt % graphene nanoparticles. For example, insome applications the graphene nanoparticle content of the polymercomposite will range between about 10 wt % and about 35 wt %. By way offurther example, in some applications the graphene nanoparticle contentof the polymer composite will range between about 12.5 wt % and about 36wt %. By way of further example, in some applications the graphenenanoparticle content of the polymer composite will range between about15 wt % and about 30 wt %.

Independent of the loading, the polymer composites of the presentinvention are characterized by a good dispersion of the graphenenanoparticles in the polymer matrix even at relatively high loadings.For example, in one embodiment, the polymer composite comprises at least5 wt % graphene nanoparticles having, on average (number average), fewerthan 50 graphene sheets per nanoparticle. By way of further example inone embodiment the polymer composite comprises at least 10 wt % graphenenanoparticles having, on average (number average), fewer than 50graphene sheets per nanoparticle. By way of further example, in oneembodiment, the polymer composite comprises at least 15 wt % graphenenanoparticles having, on average (number average), fewer than 50graphene sheets per nanoparticle. By way of further example in oneembodiment, the polymer composite comprises at least 20 wt % graphenenanoparticles having, on average (number average), fewer than 50graphene sheets per nanoparticle. By way of further example, in oneembodiment the polymer composite comprises at least 25 wt % graphenenanoparticles having, on average (number average), fewer than 50graphene sheets per nanoparticle. By way of further example in oneembodiment the polymer composite comprises, at least 30 wt % graphenenanoparticles having, on average (number average), fewer than 50graphene sheets per nanoparticle. By way of further example, in oneembodiment, the polymer composite comprise at least 35 wt % graphenenanoparticles having, on average (number average), fewer than 50graphene sheets per nanoparticle. By way of further example in oneembodiment, the polymer composite comprises at least 40 wt % graphenenanoparticles having, on average (number average), fewer than 50graphene sheets per nanoparticle. By way of further example, in oneembodiment, the polymer composite comprises at least 5 wt % graphenenanoparticles having, on average (number average), fewer than 25graphene sheets per nanoparticle. By way of further example in oneembodiment, the polymer composite comprises at least 10 wt % graphenenanoparticles having, on average (number average), fewer than 25graphene sheets per nanoparticle. By way of further example, in oneembodiment, the polymer composite comprises at least 15 wt % graphenenanoparticles having, on average (number average), fewer than 25graphene sheets per nanoparticle. By way of further example in oneembodiment, the polymer composite comprises at least 20 wt % graphenenanoparticles having, on average (number average), fewer than 25graphene sheets per nanoparticle. By way of further example, in oneembodiment, the polymer composite comprises at least 25 wt % graphenenanoparticles having, on average (number average), fewer than 25graphene sheets per nanoparticle. By way of further example in oneembodiment, the polymer composite comprises at least 30 wt % graphenenanoparticles having, on average (number average), fewer than 25graphene sheets per nanoparticle. By way of further example, in oneembodiment, the polymer composite comprises at least 35 wt % graphenenanoparticles having, on average (number average), fewer than 25graphene sheets per nanoparticle. By way of further example in oneembodiment, the polymer composite comprises at least 40 wt % graphenenanoparticles having, on average (number average), fewer than 25graphene sheets per nanoparticle. By way of further example, in oneembodiment, the polymer composite comprises at least 5 wt % graphenenanoparticles having, on average (number average), fewer than 10graphene sheets per nanoparticle. By way of further example in oneembodiment, the polymer composite comprises at least 10 wt % graphenenanoparticles having, on average (number average), fewer than 10graphene sheets per nanoparticle. By way of further example, in oneembodiment the polymer composite comprises at least 15 wt % graphenenanoparticles having, on average (number average), fewer than 10graphene sheets per nanoparticle. By way of further example in oneembodiment, the polymer composite comprises at least 20 wt % graphenenanoparticles having, on average (number average), fewer than 10graphene sheets per nanoparticle. By way of further example, in oneembodiment, the polymer composite comprises at least 25 wt % graphenenanoparticles having, on average (number average), fewer than 10graphene sheets per nanoparticle. By way of further example in oneembodiment, the polymer composite comprises at least 30 wt % graphenenanoparticles having, on average (number average), fewer than 10graphene sheets per nanoparticle. By way of further example, in oneembodiment, the polymer composite comprises at least 35 wt % graphenenanoparticles having, on average (number average), fewer than 10graphene sheets per nanoparticle. By way of further example in oneembodiment, the polymer composite comprises at least 40 wt % graphenenanoparticles having, on average (number average), fewer than 10graphene sheets per nanoparticle. By way of further example, in oneembodiment, the polymer composite comprises at least 5 wt % graphenenanoparticles having, on average (number average), 3 to 8 graphenesheets per nanoparticle. By way of further example in one embodiment,the polymer composite comprises at least 10 wt % graphene nanoparticleshaving, on average (number average), 3 to 8 graphene sheets pernanoparticle. By way of further example, in one embodiment, the polymercomposite comprises at least 15 wt % graphene nanoparticles having, onaverage (number average), 3 to 8 graphene sheets per nanoparticle. Byway of further example in one embodiment, the polymer compositecomprises at least 20 wt % graphene nanoparticles having, on average(number average), 3 to 8 graphene sheets per nanoparticle. By way offurther example, in one embodiment, the polymer composite comprises atleast 25 wt % graphene nanoparticles having, on average (numberaverage), 3 to 8 graphene sheets per nanoparticle. By way of furtherexample in one embodiment, the polymer composite comprises at least 30wt % graphene nanoparticles having, on average (number average), 3 to 8graphene sheets per nanoparticle. By way of further example, in oneembodiment, the polymer composite comprises at least 35 wt % graphenenanoparticles having, on average (number average), 3 to 8 graphenesheets per nanoparticle. By way of further example in one embodiment,the polymer composite comprises at least 40 wt % graphene nanoparticleshaving, on average (number average), 3 to 8 graphene sheets pernanoparticle.

The polymer comprised by the polymer composites of the present inventionare preferably a step-growth polymer (that is, a polymer formed bystep-growth polymerization). In one exemplary embodiment, the polymer isa homopolymer or a copolymer comprising the residues of two or moremonomers. For example, in one embodiment the polymer is a homopolymer.By way of further example, in one embodiment the polymer is a randomcopolymer comprising the residues of two or more monomers. By way offurther example, in one embodiment the polymer is a block copolymercomprising at least two polymer blocks comprising the residues ofdifferent monomers. By way of further example, in one embodiment thepolymer is a block copolymer comprising at least three polymer blockscomprising the residues of different monomers.

The polymer comprised by the polymer composites may have a range ofmolecular weights. Typically, the polymer component will have an averagemolecular weight (M_(w)) of at least about 10,000. In certainembodiments, the polymer component of the polymer composite will have anaverage molecular weight (M_(w)) of at least about 17,000. In general,however, the polymer component of the polymer composite will have anaverage molecular weight (M_(w)) of less than about 100,000.

Generally speaking, the polymers comprised by the polymer composites arerigid, substantially linear, thermally stable aromatic/heterocyclicpolymers. In one embodiment, a majority of the repeat units of thepolymer are para-catenated, i.e., the exocyclic bonds of thearomatic/heterocyclic moieties within the repeat unit have a catenationangle of 180°.

In one embodiment at least 50 wt % of the polymeric component of thepolymer composite are repeat units in which all exocyclic bonds of thearomatic/heterocyclic moieties within the repeat unit have a catenationangle of 180°. By way of further example, in one embodiment at least 60wt % of the polymeric component of the polymer composite are repeatunits in which all exocyclic bonds of the aromatic/heterocyclic moietieswithin the repeat unit have a catenation angle of 180°. By way offurther example, in one embodiment at least 70% of the polymeric repeatunits have a catenation angle of 180°. By way of further example, in oneembodiment at least 80 wt % of the polymeric component of the polymercomposite are repeat units in which all exocyclic bonds of thearomatic/heterocyclic moieties within the repeat unit have a catenationangle of 180°. By way of further example, in one embodiment at least 90wt % of the polymeric component of the polymer composite are repeatunits in which all exocyclic bonds of the aromatic/heterocyclic moietieswithin the repeat unit have a catenation angle of 180°.

In some embodiments, the polymer may contain a significant fraction ofrepeat units in which all exocyclic bonds of the aromatic/heterocyclicmoieties within the polymer repeat units have a catenation angle fallingwithin the range of 145° to 215°. For example, in one embodiment,polymer repeat units in which all exocyclic bonds of thearomatic/heterocyclic moieties within the repeat units have a catenationangle falling within the range of 145° to 215° constitute at least 60 wt% of the polymer. By way of further example, in one embodiment polymerrepeat units in which all exocyclic bonds of the aromatic/heterocyclicmoieties within the repeat units have a catenation angle falling withinthe range of 145° to 215° constitute at least 70 wt % of the polymer. Byway of further example, in one embodiment polymer repeat units in whichall exocyclic bonds of the aromatic/heterocyclic moieties within therepeat units have a catenation angle falling within the range of 145° to215° constitute at least 80 wt % of the polymer. By way of furtherexample, in one embodiment polymer repeat units in which all exocyclicbonds of the aromatic/heterocyclic moieties within the repeat units havea catenation angle falling within the range of 145° to 215° constituteat least 90 wt % of the polymer. In each of the foregoing embodiments,the polymer repeat units in which all exocyclic bonds of thearomatic/heterocyclic moieties within the repeat units have a catenationangle falling within the range of 145° to 215° may be rigid rod polymerrepeat units or extended rod polymer repeat units provided at least 50wt % of the polymer is derived from rigid rod polymer repeat units.

In some embodiments, the polymer component of the polymer composite ispredominantly comprised of rigid rod polymer repeat units and extendedrod polymer repeat units. For example, in one embodiment at least 55 wt% of the polymer is derived from extended rod polymer repeat units orrigid rod polymer repeat unit. By way of further example, in oneembodiment at least 60 wt % of the polymer is derived from extended rodpolymer repeat units or rigid rod polymer repeat units. By way offurther example, in one embodiment at least 65 wt % of the polymer isderived from extended rod polymer repeat units or rigid rod polymerrepeat units. By way of further example, in one embodiment at least 70wt % of the polymer is derived from extended rod polymer repeat units orrigid rod polymer repeat units. By way of further example, in oneembodiment at least 75 wt % of the polymer is derived from extended rodpolymer repeat units or rigid rod polymer repeat units. By way offurther example, in one embodiment at least 80 wt % of the polymer isderived from extended rod polymer repeat units or rigid rod polymerrepeat units. By way of further example, in one embodiment at least 85wt % of the polymer is derived from extended rod polymer repeat units orrigid rod polymer repeat units. By way of further example, in oneembodiment at least 90 wt % of the polymer is derived from extended rodpolymer repeat units or rigid rod polymer repeat units. In each of theforegoing exemplary embodiments, the rigid rod polymer repeat unitspreferably constitute at least 55 wt % or more of the polymer. Forexample, in one embodiment at least 60 wt % of the polymer is derivedfrom extended rod polymer repeat units and rigid rod polymer repeatunits with at least 55 wt % of the polymer being derived from rigid rodpolymer repeat units. By way of further example, in one embodiment atleast 70 wt % of the polymer is derived from extended rod polymer repeatunits and rigid rod polymer repeat units with at least 55 wt % of thepolymer being derived from rigid rod polymer repeat units. By way offurther example, in one embodiment at least 80 wt % of the polymer isderived from extended rod polymer repeat units and rigid rod polymerrepeat units with at least 60 wt % of the polymer being derived fromrigid rod polymer repeat units. By way of further example, in oneembodiment at least 90 wt % of the polymer is derived from extended rodpolymer repeat units and rigid rod polymer repeat units with at least 55wt % of the polymer being derived from rigid rod polymer repeat units.By way of further example, in one embodiment at least 90 wt % of thepolymer is derived from extended rod polymer repeat units and rigid rodpolymer repeat units with at least 55 wt % of the polymer being derivedfrom rigid rod polymer repeat units. In one embodiment at least 90 wt %of the polymer is derived from extended rod polymer repeat units andrigid rod polymer repeat units with at least 60 wt % of the polymerbeing derived from rigid rod polymer repeat units. By way of furtherexample, in one embodiment at least 90 wt % of the polymer is derivedfrom extended rod polymer repeat units and rigid rod polymer repeatunits with at least 70 wt % of the polymer being derived from rigid rodpolymer repeat units. By way of further example, in one embodiment atleast 90 wt % of the polymer is derived from extended rod polymer repeatunits and rigid rod polymer repeat units with at least 80 wt % of thepolymer being derived from rigid rod polymer repeal units.

In one embodiment, the polymer comprised by the polymer composite is arigid-rod polymer or a rigid-rod/extend rod copolymer. Rigid rodpolymers are typically characterized by high tensile strength, highmodulus, stiffness, and thermal stability. Such polymers are alsosometimes referred to as liquid crystal extended chain polymers. In onesuch embodiment the polymer composite comprises a homopolymer or acopolymer containing rigid rod polymer repeat units corresponding toFormula 1 or Formula 2:

wherein the A¹ ring is a six-membered aromatic or a six-memberedheterocyclic ring, Y is —O—, —S— or —NR′, R′ is hydrogen, hydrocarbyl,substituted hydrocarbyl or acyl, and X₁ and X₂ are independently a bond,para-ordered aryl or para-ordered heterocyclic ring.

In one embodiment, the polymer composite comprises a homopolymer or acopolymer containing rigid rod polymer repeat units corresponding toFormula 1 or Formula 2 wherein the A¹ ring is selected from the groupconsisting of

and the polymer composite comprises a homopolymer or a copolymercontaining rigid rod polymer repeat units corresponding to Formula 1A,1B, 1C, 1D, 2A, 2B, 2C, or 2D:

wherein Y is —O—, —S— or —NR′, R′ is hydrogen, hydrocarbyl, substitutedhydrocarbyl or acyl, and X₁ and X₂ are independently a bond,para-ordered aryl or para-ordered heterocyclic ring. In one suchembodiment, X₁ and X₂ are each a bond. In another such embodiment, oneof X₁ and X₂ is a bond and the other is optionally substitutedpara-ordered arylene or optionally substituted para-ordered heterocyclecorresponding to Formula 3

wherein n is 0-4, each R₂ is independently hydrogen, hydrocarbyl,substituted hydrocarbyl, hydroxy, halo, phospho (—PO₃H), or sulfo(—SO₃H), and “*” designates the point of attachment of the A² ringsystem to the remainder of the repeat unit. For example, in oneembodiment, the A² ring system is an optionally substituted phenylene,pyridine, pyran, thiopyran, diazine, oxazine, thiamine, dioxine,triazine or tetrazine ring. By way of further example, in oneembodiment, one of X₁ and X₂ is a bond and the other is optionallysubstituted para-ordered phenylene or an optionally substitutedpara-ordered six-membered heterocycle corresponding to Formula 3A, 3B or3C

wherein n is 0-4, each R₂ is independently hydrogen, hydrocarbylsubstituted hydrocarbyl, hydroxy, halo, phospho (—PO₃H), or sulfo(—SO₃H), and “*” designates the point of attachment of the A² ringsystem to the remainder of the repeat unit. In another embodiment, theA² ring system is a benzobisazole of Formula 4A or Formula 5A, or aheterocyclobisazole of Formula 4B, 4C, 4D, 5B, 5C or 5D:

wherein Y is —O—, —S— or —NR′, R′ is hydrogen, hydrocarbyl, substitutedhydrocarbyl or acyl, and “*” designates the point of attachment of thering system of Formula 4A, 4B, 4C, 4D, 5A, 5B, 5C or 5D to the remainderof the repeat unit. By way of further example, in another embodiment X₁and X₂ are independently optionally substituted para-ordered arylene oroptionally substituted para-ordered heterocycle corresponding to Formula3.

In one embodiment in which the polymer composite comprises a homopolymeror a copolymer containing rigid rod polymer repeat units correspondingto Formula 1A, 1B, 1C, 1D, 2A, 2B, 2C or 2D, Y is —S— and thehomopolymer or copolymer contains rigid rod polymer repeat unitscorresponding to Formula 1E, 1F, 1G, 1H, 2E, 2F, 2G, or 2H

wherein X₁ and X₂ are independently a bond, para-ordered aryl orpara-ordered heterocyclic ring. In one such embodiment, X₁ and X₂ areeach a bond. In another such embodiment, one of X₁ and X₂ is a bond andthe other is optionally substituted para-ordered arylene or optionallysubstituted para-ordered heterocycle corresponding to Formula 3

wherein n is 0-4, each R₂ is independently hydrogen, hydrocarbyl,substituted hydrocarbyl, hydroxy, halo, phospho (—PO₃H), or sulfo(—SO₃H), and “*” designates the point of attachment of the A² ringsystem to the remainder of the repeat unit. For example, in oneembodiments, the A² ring system is an optionally substituted phenylene,pyridine, pyran, thiopyran, diazine, oxazine, thiamine, dioxine,triazine or tetrazine ring. By way of further example, in oneembodiment, one of X₁ and X₂ is a bond and the other is optionallysubstituted para-ordered phenylene or an optionally substitutedpara-ordered six-membered heterocyclic corresponding to Formula 3A, 3Bor 3C

wherein n is 0-4, each R₂ is independently hydrogen, hydrocarbyl,substituted hydrocarbyl, hydroxy, halo, phospho (—PO₃H), or sulfo(—SO₃H), and “*” designates the point of attachment of the A² ringsystem to the remainder of the repeat unit. In another embodiment, theA² ring system is a benzobisazole of Formula 4A or Formula 5A, or ahetero-cyclobisazole of Formula 4B, 4C, 4D, 5B, 5C or 5D:

wherein Y is —O—, —S— or —NR′, R′ is hydrogen, hydrocarbyl, substitutedhydrocarbyl or acyl, and “*” designates the point of attachment of thering system of Formula 4A, 4B, 4C, 4D, 5A, 5B, 5C or 5D to the remainderof the repeat unit. By way of further example, in another embodiment X₁and X₂ are independently optionally substituted para-ordered arylene oroptionally substituted para-ordered heterocycle corresponding to Formula3.

In one embodiment in which the polymer composite comprises a homopolymeror a copolymer containing rigid rod polymer repeat units correspondingto Formula 1A, 1B, 1C, 1D, 2A, 2B, 2C or 2D, Y is —N— and thehomopolymer or copolymer contains rigid rod polymer repeat unitscorresponding to Formula 1I, 1J, 1K, 1L, 2I, 2J, 2K, or 2L

wherein R′ is hydrogen, hydrocarbyl, substituted hydrocarbyl or acyl, X₁and X₂ are independently a bond, para-ordered aryl or para-orderedheterocyclic ring. In one such embodiment X₁ and X₂ are each a bond. Inanother such embodiment, one of X₁ and X₂ is a bond and the other isoptionally substituted para-ordered arylene or optionally substitutedpara-ordered heterocycle corresponding to Formula 3

wherein n is 0-4, each R₂ is independently hydrogen, hydrocarbyl,substituted hydrocarbyl, hydroxy, halo, phospho (—PO₃H), or sulfo(—SO₃H), and “*” designates the point of attachment of the A² ringsystem to the remainder of the repeat unit. For example, in oneembodiment, the A² ring system is an optionally substituted phenylene,pyridine, pyran, thiopyran, diazine, oxazine, thiamine, dioxine,triazine or tetrazine ring. By way of further example, in oneembodiment, one of X₁ and X₂ is a bond and the other is optionallysubstituted para-ordered phenylene or an optionally substitutedpara-ordered six-membered heterocyclic corresponding to Formula 3A, 3Bor 3C

wherein n is 0-4, each R₂ is independently hydrogen, hydrocarbyl,substituted hydrocarbyl, hydroxy, halo, phospho (—PO₃H), or sulfo(—SO₃H), and “*” designates the point of attachment of the A² ringsystem to the remainder of the repeat unit. In another embodiment, theA² ring system is a benzobisazole of Formula 4A or Formula 5A, or aheterocyclobisazole of Formula 4B, 4C, 4D, 5B, 5C or 5D:

wherein Y is —O—, —S— or —NR′, R′ is hydrogen, hydrocarbyl, substitutedhydrocarbyl or acyl, and “*” designates the point of attachment of thering system of Formula 4A, 4B, 4C, 4D, 5A, 5B, 5C or 5D to the remainderof the repeat unit. By way of further example, in another embodiment X₁and X₂ are independently optionally substituted para-ordered arylene oroptionally substituted para-ordered heterocycle corresponding to Formula3.

In one embodiment in which the polymer composite comprises a homopolymeror a copolymer containing rigid rod polymer repeat units correspondingto Formula 2I, 2J, 2K, or 2L, X₁ and one of the R′ substituents combineto form a fused heterocyclic ring stem and the other R′ is acyl wherebythe repeat unit is ladder repeat unit. One such repeat unit is thebenzamidazobenzophenanthroline (“BBL”) repeat unit corresponding toFormula 6

as described in U.S. Pat. No. 3,632,414, incorporated by referenceherein in its entirety.

Examples of benzobisazole polymers comprised by the polymer-compositeinclude para-ordered heterocyclic polymer having repeat group of theformula

where Y is —S—, n is 1 or 2, and R is a hydroxyl group, a sulfo group oran alkyl group having 1 to 4 carbon atoms.

Other examples of rigid rod polymers comprised by the polymer compositeinclude benzimidazole polymers and copolymers comprising repeat units ofthe formula

and include p-phenylenebenzimidazole (PBI) comprising repeat units ofthe formula

Such polymers and copolymers are described in U.S. Pat. No. 3,901,855and incorporated by reference herein in its entirety.

Further examples of benzobisazole polymers comprised by the polymercomposite are polybenzobisoxazole polymers and copolymers comprisingrepeat units of the formula

and include polymers and copolymers of p-phenylenebenzobisoxazole (PBO)comprising repeat units of the formula

Further examples of benzobisazole polymers comprised by the polymercomposite are polybenzobisthiazole polymers and copolymers comprisingrepeat units of the formula

and include polymers and copolymers of p-phenylenebenzobisthiazole(PBZT) comprising repeat units of the formula

both described in U.S. Pat. No. 4,533,693, incorporated by referenceherein in its entirety.

Further examples of benzobisazole polymers comprised by the polymercomposite are those p-phenylenebenzobisazole polymers and copolymerscontaining pendant substituents on the phenylene group, includingphenylenebenzobisazoles with pendant hydroxyl groups, such asdihydroxyphenylene-benzobisoxazole (Di-OH PBO), comprising repeat unitsof the formula

dihydroxy-phenylenebenzobisthiazole (Di-OH PBZT), comprising repeatunits of the formula

dibydroxy-phenylenebenzobisimidazole (Di-OH PBI) comprising repeat unitsof the formula

described in U.S. Pat. Nos. 5,041,522 and 5,039,778, each incorporatedby reference herein in its entirety, anddihydroxy-phenylenepyridobisimidazole (Di-OH PPBI) comprising repeatunits of the formula

described in U.S. Pat. No. 5,674,969, incorporated by reference hereinin its entirety.

Further examples of polymers comprised by the polymer composite includephenylenebenzobisazoles having pendant sulfonic acid groups, such assulfo-phenylenebenzobisoxazole (sulfo-PBO) comprising repeat units ofthe formula

sulfo-phenylenebenzobisimidazole (sulfo-PBI) comprising repeat units ofthe formula

and sulfo-phenylenebenzobisthiazole (sulfo-PBZT) comprising repeat unitsof the formula

described in U.S. Pat. Nos. 5,312,876 and 5,312,895, each incorporatedby reference herein its entirety. Also included arephenylenebenzobisazole polymers with pendant methyl groups, such asmethyl- and dimethyl-phenylenebenzobisoxazole (Me-PBO) comprising repeatunits of formula

wherein R and R′ are each hydrogen or methyl one of R and R′ is hydrogenand the other is methyl or R and R′ are each methyl. Also included aremethyl- or dimethyl-phenylenebenzobisthiazole (Me-PBZT), comprisingrepeal units of the formula

wherein R and R′ are each hydrogen or methyl one of R and R′ is hydrogenand the other is methyl or R and R′ are each methyl. Also included aremethyl- and dimethyl-phenylenebenzobisimidazole (Me-PBI), comprisingrepeat units of the formula

where in R and R′ are each hydrogen of methyl, one of R and R′ ishydrogen and the other is methyl or R and R′ are each methyl asdescribed in U.S. Pat. Nos. 5,001,217, 5,098,988, and 5,136,012, eachincorporated by reference herein in its entirety.

In some embodiments, the polymer comprised by the polymer composite is arigid rod copolymer comprising rigid rod polymer repeat units andextended rod polymer repeat units. Exemplary rigid rod polymerscomprising rigid rod polymer repeat units and extended rod polymerrepeat units include, but are not limited to, polymers and copolymershaving extended rod polymer repeat units of the formula

wherein the A¹ ring is a six-membered aromatic or a six-memberedheterocyclic ring, Y is —O—, —S— or —NR′, R′ is hydrogen, hydrocarbyl,substituted hydrocarbyl or acyl, X³ is an imidazole, pyrazole orthiopene ring, and Z is selected from the group consisting of —NR″, S,and O, and R″ is hydrogen, hydrocarbyl, or substituted hydrocarbyl oracyl. For example, in one embodiment, R″ is hydrogen or phenyl.Exemplary extended rod polymer repeat units include the following repeatunits

wherein Y is —O—, —S— or —NR′, R′ is hydrogen, hydrocarbyl, substitutedor hydrocarbyl.

Such extended rod copolymers may be polymerized in situ in the presenceof the rigid rod polymers generally described in Formulae 1 and 2 aboveto produce an aromatic heterocyclic block copolymer having rigid andextended rod segments of the general formula

wherein Y and Z are the same or different and are selected from thegroup consisting of —S—, —O—, and —NR₂, each R₂ is independentlyhydrogen, hydrocarbyl, substituted hydrocarbyl, hydroxy, halo, phospho(—PO₃H), or sulfo (—SO₃H); m is an integer equal to the number of repeatunits of the rigid segment and n is an integer equal to the repeat unitsof the extended rod segments. In one exemplary embodiment at least oneof Y and Z is —NR₂ and R₂ is hydrogen or phenyl. The method ofpreparation of the aromatic heterocyclic copolymer is described in U.S.Pat. No. 4,544,713, incorporated by reference herein in its entirety. Ingeneral, and relative to a homopolymer of the corresponding rigid rodpolymer repeat units, the block copolymer may have an increasedelongation to break property, and/or increased solubility in the acidsolvents.

Another example of block copolymers comprised by the polymer compositeinclude aromatic heterocyclic block copolymers having rigid and extendedrod segments of the general formula

wherein Y and Z are the same or different and are selected from thegroup consisting of —S', —O—, and —NR₂, each R₂ is independentlyhydrogen, hydrocarbyl, substituted hydrocarbyl, hydroxy, halo, phospho(—PO₃H), or sulfo (—SO₃H); m is an integer equal to the number of repeatunits of the rigid segment and n is an integer equal to the repeat unitsof the extended rod segments. In one exemplary embodiment, at least oneof Y and Z is —NR₂ and R₅ is hydrogen or phenyl.

Other examples of aromatic heterocyclic block copolymers having rigidand extended rod segments includes copolymers of the formula

wherein Y and Z are the same or different and are selected from thegroup consisting of —S—, —O—, and —NR₂, m is an integer equal to thenumber of repeat units of the rigid segment, n is an integer equal tothe repeat units of the extended rod segments, R is hydroxy, sulfo(—SO₃H), or an alkyl group having 1 to 4 carbon atoms, each R₂ isindependently hydrogen, hydrocarbyl, substituted hydrocarbyl, hydroxy,halo, phospho (—PO₃H), or sulfo (—SO₃H) and t is 1-4. In one exemplaryembodiment, at least one of Y and Z is —NR₂ and R₂ is hydrogen orphenyl.

Another example of aromatic heterocyclic block copolymers having rigidand extended rod segments includes copolymers of the general formula

wherein Y and Z are the same or different and are selected from thegroup consisting of —S—, —O—, and —NR₂, m is an integer equal to thenumber of repeat units of the rigid segment, n is an integer equal tothe repeat units of the extended rod segments, R is hydroxy, sulfo(—SO₃H), or an alkyl group having 1 to 4 carbon atoms each R₂ isindependently hydrogen, hydrocarbyl, substituted hydrocarbyl, hydroxy,halo, phospho (—PO₃H), or sulfo (—SO₃H) and t is 1-4. In one exemplaryembodiment, at least one of Y and Z is —NR₂ and R₂ is hydrogen orphenyl,

Other examples of the aromatic heterocyclic block copolymers havingrigid rod and extended rod segments includes copolymers of the generalformates.

wherein Y and Z are the same or different and are selected from thegroup consisting of —S—, —O—, and —NR₂; m is an integer equal to thenumber of repeat units of the rigid segment, n is an integer equal tothe repeat units of the extended rod segments, and each R₂ isindependently hydrogen, hydrocarbyl, substituted hydrocarbyl, hydroxy,halo, phospho (—PO₃H), or sulfo (—SO₃H). In one exemplary embodiment, atleast one of Y and Z is —NR₂ and R₂ is hydrogen or phenyl.

Other aromatic heterocyclic block copolymers having rigid rod andextended rod segments includes copolymers of the general formulas

wherein Y and Z are the same or different and are selected from thegroup consisting of —S—, —O—, and —NR₂; m is an integer equal to thenumber of repeat units of the rigid segment, and n is an integer equalto the repeat units of the extended rod segments, and each R₂ isindependently hydrogen, hydrocarbyl, substituted hydrocarbyl, hydroxy,halo, phospho (—PO₃H), or sulfo (—SO₃H). In one exemplary embodiment, atleast one of Y and Z is —NR₂ and R₂ is hydrogen or

In another embodiment, the polymer of the polymer composite may furthercomprise a non-extended/rigid rod polymer or polymer segmentincorporated through step-growth polymerization. The non-extended/rigidrod polymer or polymer segment may constitute up to 25 wt % of thepolymer component of the polymer composite. In one exemplary embodiment,the non-extended/rigid rod polymer is a homopolymer or a copolymercomposing the residues of two or more monomers having repeat units thatdiffer from other polymers or other polymer segments in the polymercomposite. By way of further example, the non-extended/rigid rod polymeris a condensation polymer. By way of further example, thenon-extended/rigid rod polymer is a condensation polymer selected fromthe group of polysulfide, polyether, polyester, or polyamide. By way offurther example, the non-extended/rigid rod polymer is polyepoxide orpoly-paraphenylene terephthalamide (Kevlar™). In a preferred embodiment,the additional polymer may be sheet-like to permit pooling in solution.Thus, for example, in one embodiment the polymer of the polymercomposite comprises a blend of a rigid rod polymer and anon-extended/rigid rod polymer. In another embodiment, the polymer ofthe polymer composite is a block copolymer with at least one of thesegments of the copolymer comprising non-extended/rigid rod polymerrepeat units. In general, when the non-extended/rigid rod polymercomprises a blend of a rigid rod polymer and a non-extended/rigid rodpolymer, the non-extended/rigid rod polymer will constitute less than 25wt % of such blend. For example, in one embodiment thenon-extended/rigid rod polymer will constitute less than 20 wt % of sucha blend. By way of further example, the non-extended/rigid rod polymerwill constitute less than 15 wt % of such a blend. By way of furtherexample, the non-extended/rigid rod polymer will constitute less than 10wt % of such a blend. By way of further example, the non-extended/rigidrod polymer will constitute less than 5 wt % of such a blend. Similarly,when the non-extended/rigid rod polymer is a block copolymer with atleast one of the segments of the copolymer comprising non-extended/rigidrod polymer repeat units, the non-extended/rigid rod polymer repeatunits will constitute less than 25 wt % of the copolymer. In someembodiments, the non-extended/rigid rod polymer repeat units willconstitute less than 20 wt % of the copolymer. In some embodiment, thenon-extended/rigid rod polymer repeat units will constitute less than 15wt % of the copolymer. In some embodiments, the non-extended/rigid rodpolymer repeat units will constitute less than 10 wt % of the copolymer.In some embodiments, the non-extended/rigid rod polymer repeat unitswill constitute less than 5 wt % of the copolymer.

In another embodiment, the polymer composite may comprise a nanoparticleother than graphene. For example, the polymer composite may compriseclay, metallic, or ceramic nanoparticles or other carbon nanoparticlessuch as carbon nanotubes in addition to graphene. In general, it ispreferred that any additional nanoparticles be sheet-like.

Polymer Synthesis

Polymer compositions comprising graphene nanoparticles and rigid-rodpolymers and copolymers may be synthesized by a range of methods. In oneexemplary method, the graphene nanoparticles are dispersed (e.g., atloading of at least 50 wt %) into the polymer matrix, and by means ofpi-pi interaction these planar sheets of graphene materials are pulledinto the polymer. In another exemplary method, rigid-rod polymers arepolymerized, in-situ, in the presence of the graphene nanoparticles. Inthis method, rigid rod monomers may be dissolved in a strong acid suchas phosphoric acid or methanesulfonic acid and oligomerized to producechains of about 5 to 10 rigid rod polymer repeat units on average.Graphene is then added to the oligomer-containing reaction mixture toform a polymer composite comprising a polymer and graphenenanoparticles. The in-situ polymerization may be done through thepolycondensation of diamines and diacid monomers (or other suitablydifunctionalized monomers) in the presence of graphene nanoparticles. Asthe rigid-rod polymers or copolymers polymerize, liquid crystallinedomains form. The graphene nanoparticles align along the propagatingrigid-rod molecules and are entrapped in the resulting dope. Theresulting anisotropic alignment of the rigid-rod polymers and graphenenanoparticles appears liquid crystalline in nature; that is, thereaction mixture appears opalescent. The present invention provides asubstantially uniform, aligned distribution of graphene nanoparticlesthat is not readily obtainable by the process of melt mixing a moltenpolymer with graphene nanoparticles.

Processing of the new compositions into fibers and films provides hybridmaterials with vastly improved tensile properties, which are superior tothe same polymers without incorporated graphene nanoparticles. Althoughnot meaning to be limited, the polymer component of the presentcompositions can include various benzamidazobenzophenanthroline,benzobisazole, and pyridobisimidazole polymers and copolymers. Films andfibers of these polymers and copolymers are known for their extremelyhigh modulus and high strength. In this invention, the rigid-rodpolymers and copolymers are formed by in-situ polymerization from thepolycondensation of diamine and diacidmonomers. Suitableamino-group-containing monomers include, but are not limited to:2,5-diamino-1,4-benzenedithiol dihydrochloride,4,6-diamino-1,3-benzenedithiol dihydrochloride,1,2,4,5-tetraaminobenzene tetrahydrochloride, 2,3,5,6-tetraaminopyridinetetrahydrochloride, 2,5-diamino-1,4-l dihydrochloride, and1,4,5,8-tetraaminonaphthalene tetrahydrochloride. Suitableacid-group-containing monomers include, but are not limited to:terephthalic acid, dihydroxy-terephthalic acid, and1,4,5,8-tetracarboxynaphthalene.

In the case of aromatic heterocyclic block copolymers, the method ofthis invention comprises the steps of preparing the rigid-rod polymerblock by reacting a diaminomonomer and terephthalic acid (in slightexcess) in polyphosphoric acid (PPA) to form a carboxy-terminated rigidrod segment, followed by addition of a copolymerizable monomer andcopolymerization of the same. The rigid rod segment containingcarboxy-terminated groups of the general formula

wherein Y is or —O—, —S— or —NR′, where R′ is hydrogen, alkyl having 1to 4 carbon atoms, or an aromatic group having 1 or 2 aromatic rings,and m is an integer equal to the number of repeat units of the rigidsegment.

Following polymerization of the above rigid rod segment monomers, acopolymerizable monomer of the general formula

wherein X is —NH₂, —OH, —SH, or —NHC₆H₅ is added to the reaction mixturecontaining the rigid rod segment, and polymerization of the extended rodsegments as well as grafting of these segments onto the rigid rodsegments is carried out.

The in-situ polymerizations and/or copolymerizations may be conducted inany suitable medium in which the rigid-rod polymers or copolymers can beformed and maintained in solution. A suitable medium for carrying outthe polycondensation polymerizations of the present invention comprisespolyphosphoric acid (PPA), having a formula represented byH_(n+2)P_(n)O_(3n+1) or HO(PO₃H)_(n)H. The polyphosphoric acidcomposition can be expressed in terms of the phosphorous pentoxide(P₂O₅) content or the phosphoric acid (H₃PO₄, n=1) content.

The polymer concentration in the medium preferably is selected topromote the formation of an anisotropic reaction mixture. Polymerconcentrations in the range from about 5 wt % to about 20 wt % in themedium can promote an anisotropic reaction mixture. The graphenenanoparticles concentration preferably can range from about 0.1 wt % toabout 70 wt % for films production and from about 1 wt % to about 50 wt% for fibers production based on the weight of polymer in thepolymerization.

In the present invention, the process for making a rigid-rodpolymer/graphene nanoparticles composition involves synthesizing therigid-rod polymer or copolymer in the presence of graphenenanoparticles. In one embodiment of in-situ polymerization,stoichiometric amounts of amine hydrochloride and acid monomers arecombined in 85% phosphoric acid and heated to a temperature in the rangeof about 60° C. to about 80° C. to effect the thermaldehydrochlorination of the amine monomer. Note that the use of amineswithout protective hydrochloride is also within the scope of thisinvention. After the dehydrochlorination is complete, the graphenenanoparticles are added. The temperature is then raised to about 100° C.and maintained for about 4 to 6 hours. The reaction temperature iscooled to about 45° C. and phosphorous pentoxide (P₂O₅) is added to mate77% PPA. After the phosphorous pentoxide addition, the temperature isincreased to 100° C. and maintained for about 4 hours. Additional P₂O₅is then added to increase the PPA concentration to about 82 to about 84%PPA. The temperature is then raised to about 165° C. and maintained atthat temperature for about 10 to 12 hours. The temperature of thereaction mixture is then raised to about 190° C. and held for about 4hours. The procedure results in a liquid crystalline compositioncomprising rigid-rod liquid crystalline polymer and graphenenanoparticles that can be extruded and processed into fiber or film.

In one embodiment of in-situ copolymerization, an excess amount of acidmonomers (preferably about 5 wt %) and amine hydrochloride are combinedin 85% phosphoric acid and heated to a temperature in the range of about60° C. to about 80° C. to effect the thermal dehydrochlorination of theamine monomer. Note that the use of amines without protectivehydrochloride is also with the scope of this invention. After thedehydrochlorination is complete, the graphene nanoparticles are added.The temperature is then raised to about 100° and maintained for about 4to 6 hours. The reaction temperature is cooled to about 45° C. andphosphorous pentoxide (P₂O₅) is added to make 77% PPA. After thephosphorous pentoxide addition, the temperature is increased to 100° C.and maintained for about 4 hours. Additional P₂O₅ is then added toincrease the PPA concentration to about 82 to about 84% PPA. Thetemperature is then raised to about 165° C. and maintained at thattemperature for about 5 hours with observed stir-opalescence. Theviscous solution is cooled to 65° C. and the carboxy-monoamine monomeris added thereto. The resulting mixture is heated slowly under inert gasatmosphere to about 100° C. for a period of about 6 to 12 hours toeffect the dehydrochlorination of the carboxy-monoamine monomer.Following the dehydrochlorination, the reaction is slowly heated back to165° C. and maintained at that temperature for 10 to 12 hours. Thetemperature of the reaction is then raised to 190° C. and held for about4 hours. The procedure results in a liquid crystalline compositioncomprising rigid-rod liquid crystalline copolymer and graphenenanoparticles that can be extruded and processed into fiber or film.

After each in-situ polymerization, aliquot samples are taken todetermine intrinsic viscosity and also for processing into cast films.The samples are precipitated into water, treated with ammoniumhydroxide, washed extensively with water, and dried under reducedpressure. After precipitating into water or redissolving of driedsamples in methanesulfonic acid for intrinsic viscosity measurements,the samples show no separation of the graphene nanoparticles from thederived polymer.

The cast or aggregated films from the rigid rod polymers andcopolymers/graphene nanoparticles composite, such as those based onbenzobisazoles, pyridobisazoles and benzamidazobenzophenanthroline, areformed from MSA (methanesulfonic acid) solution. The added graphenenanoparticles concentration preferably can range from about 0.1 wt % toabout 50 wt % based on the weight of the polymer or copolymer in MSA.Generally, the films of the present invention comprising rigid-rodpolymer or copolymer/graphene nanoparticles composites havesignificantly higher strength and tensile properties, such as higherstiffness, tensile modulus, and strain to failure (elongation-to-break),than like polymer films without graphene nanoparticles. Certain filmscomprising the rigid-rod polymers/graphene nanoparticles composites ofthis invention have shown about 350% greater tensile strength than overfilms of the same polymeric composition without graphene nanoparticles.Films prepared with the compositions of this invention also show lowercreep than like polymer films without graphene nanoparticles.

Fiber spinning may be done by any suitable technique. One such method isdry-jet wet spinning using a piston driven spinning system. For fiberspinning solution or dope, the added graphene nanoparticlesconcentration preferably can range from about 1 wt % to about 50 wt %based on the weight of the polymer or copolymer in PPA medium. Thetemperature the polymer or copolymer composite solution or dopepreferably is maintained between about 100° C. and about 150° C. An airgap preferably is maintained in the range of about 2 cm and about 25 cm.Extruded fiber is coagulated in water at room temperature. Fiber iswashed in water, dilute base, and water again for about a week or forany time sufficient to remove the acid from the fiber. The fiber issubsequently dried in vacuum at about 80° C. Dried fiber can beheat-treated in nitrogen at about 400° C. to impart higher strength andtensile properties. Generally, the fibers of the present inventioncomprising rigid-rod polymer/graphene nanoparticles composites havesignificantly higher strength and tensile properties, such as higherstiffness and strain to failure (elongation to break), than like polymerfibers without graphene nanoparticles. Certain fibers comprising therigid-rod polymers/graphene nanoparticles composites of this inventionhave shown about 230% greater tensile strength than over fibers of thesame polymeric composition without graphene nanoparticles. Fibersprepared with the compositions of this invention also show lower creepthan like polymer fibers without graphene nanoparticles.

This composite of this invention provides a fundamental improvement inproducts and articles of manufacture comprising rigid-rod polymers andcopolymers, and it enables new and improved articles, of manufacture,including, but not limited to composite structural materials, films,coatings and fibers requiring high tensile strength such as forhigh-strength fibers and structural elements of machines, buildings, andvehicles. Improved articles of manufacture incorporating fibers of thepresent invention include body armor, bullet-proof vests, vehiculararmor, armor for structures, elements of ballistic protection systemsand as reinforcing fibers for both organic and inorganic products, suchas in tires, belts, ceramics, polymer laminates for aircraft and othercompositions requiring high strength on the grapheme nanoparticlesconcentration and dispersion, additional properties of electrical orthermal conductivity, electromagnetic and radio-frequency shielding mayalso be realized.

EXAMPLES

The following non-limiting examples are provided to further illustratethe present invention. It should be appreciated by those of skill in theart that the techniques disclosed in the examples that follow representapproaches the inventors have found function well in the practice of theinvention, and thus can be considered to constitute examples of modesfor its practice. However, those of skill in the art should, in light ofthe present disclosure, appreciate that many changes can be made in thespecific embodiments that are disclosed and still obtain a like orsimilar result without departing from the spirit and scope of theinvention.

Example I

BBL/GS (80/20)

A composition of 20% graphene nanoparticles and 80% ladder polymer,benzimidazobenzo-phenanthroline (BBL) was prepared as follows. Into thebottom of a 250-ml resin flask equipped with a mechanical stirrer, anitrogen inlet and outlet, was placed 5.6804 g (0.02 mol) of1,2,4,5-tetraaminobenzene tetrahydrochloride, 6.0842 g (0.02 mol) of1,4,5,8-naphtalenetetracarboxylic acid, and 16.16 g of phosphoric acid(85%). The resulting mixture was dehydrochlorinated under nitrogenatmosphere at 65° C. for 16 hours. The temperature was then raised to80° C. and held for 4 hours. 1.32 g of graphene nanoparticles (chemicalsynthesized graphene nanoparticles from Angstrom, Inc., Dayton, Ohio)was added to the mixture. The mixture was heated at 100° C. for 16 hoursand then cooled to room temperature. 10.69 g of P₂O₅ was added to themixture to generate polyphosphoric acid (77% P₂O₅). The mixture wasstirred for 2 hours at 80° C. and cooled to room temperature. 20.02 g ofP₂O₅ was added to the mixture to bring the polymer concentration to 12%.The mixture was then heated at 160° C. for 16 hours. As the temperatureincreased, stir opalescence began to occur at about 160° C. The mixturewas finally heated to 190° C. and held for additional 4 hours. Analiquot of the polymer dope was precipitated in water, broken up with ablender, collected by suction filtration, washed with water and driedunder reduced pressure (0.02 mmHg) at 100° C. for 24 hours. An intrinsicviscosity of 17.0 dl/g was determined in methanesulfonic acid at 30° C.

Example II

PBZT/GS (90/10)

A composition of 10% graphene nanoparticles (GS) and 90%polyphenylenebenzobisthiazole (PBZT) was prepared as follows. Into thebottom of a 250-ml resin flask equipped with a mechanical stirrer, anitrogen inlet and outlet, was placed 4.904 g (0.02 mol) of2,5-diamino-1,4-benzenedithiol dihydrochloride, 3.3226 g (0.02 mol) of2,5-dihydroxyterepthalic acid, and 20.68 g of phosphoric acid (85%). Theresulting mixture was dehydrochlorinated under nitrogen atmosphere at65° C. for 16 hours. The temperature was then raised to 80° C. and heldfor 4 hours. 0.52 g of purified graphene nanoparticles (chemicalsynthesized graphene nanoparticles from Angstrom, Inc., Dayton, Ohio)was added to the mixture. The mixture was heated at 100° C. for 16 hoursand then cooled the mixture to room temperature, 13.69 g P₂O₅ was addedto the mixture to generate polyphosphoric acid (77% P₂O₅). The mixturewas stirred for 2 hours at 80° C. and then cooled to room temperature.12.13 g of P₂O₅ was added to the mixture to bring the polymerconcentration to 10%. The mixture was heated at 160° C. for 16 hours. Asthe temperature increased, stir opalescence began to occur at about 150°C. The mixture was finally heated to 190° C. and held for an additional4 hours. An aliquot of the polymer dope was precipitated in water,broken up with a blender, collected by suction filtration, washed withwater and dried under reduced pressure (0.02 mmHg) at 100° C. for 24hours. An intrinsic viscosity of 26 dl/g was determined inmethanesulfonic acid at 30° C.

Example III

PBO/GS (95/5)

A composition of 5% of graphene nanoparticles (GS) and 95%polyphenylenebenzobisoxazole (PBO) was prepared as follows. Into thebottom of a 250-ml resin flask equipped with a mechanical stirrer, anitrogen inlet and outlet, was place 4.2612 g (0.02 mol) of1,4-diaminoresorcinol dihydrochloride, 4.0605 g (0.02 mol) ofterephthaloyl chloride, and 12.14 g of phosphoric acid (85%). Theresulting mixture dehydrochlorinated under nitrogen atmosphere at 65° C.for 16 hours. The temperature was then raised to 80° C. and held for 4hours. 0.23 g of purified graphene nanoparticles (chemical synthesizedgraphene nanoparticles from Angstrom, Inc., Dayton, Ohio) was added tothe mixture. The mixture was heated at 100° C. for 16 hours and thencooled to room temperature. 8.04 g of P₂O₅ was added to the mixture togenerate polyphosphoric acid (77% P₂O₅). The mixture was stirred for 2hours at 80° C. and then cooled to room temperature. 7.15 g of P₂O₅ wasadded to the mixture to bring the polymer concentration to 14%. Themixture was heated at 160° C. for 16 hours. As the temperatureincreased, stir opalescence began to occur at about 155° C. The mixturewas finally heated to 190° C., for an additional 4 hours. An aliquot ofthe polymer dope was precipitated in water, broken up with a blender,collected by suction filtration, washed with water and dried underreduced pressure (0.02 mmHg) at 100° C. for 24 hours. An intrinsicviscosity of 18 dl/g was determined in methanesulfonic acid, at 30° C.

Example IV

Di-OHPBO/GS (90/10)

A composition of 10% graphene nanoparticles and 90%2,5-dihydroxy-polyphenylenebenzobisoxazole (2,5-Di-OH PBO) was preparedas follows. Into the bottom of a 250-ml resin flask equipped with amechanical stirrer, a nitrogen inlet and outlet, was placed 4.2612 g(0.02 mol) of 1,4-diaminoresorcinol dihydrochloride, 4.7004 g (0.02 mol)of 2,5-dihydroxyterephthaloyl chloride, and 12.14 g of phosphoric acid(85%). The resulting mixture was dehydrochlorinated under nitrogenatmosphere at 65° C. for 16 hours. The temperature was then raised to80° C. and held for 4 hours. 0.47 g of graphene nanoparticles (chemicalsynthesized graphene nanoparticles from Angstrom, Inc., Dayton, Ohio)was added to the mixture. The mixture was heated at 100° C. for 16 hoursand then cooled the mixture to room temperature. 9.14 g of P₂O₅ wasadded to the mixture to generate polyphosphate acid (77% P₂O₅). Themixture was stirred for 2 hours at 80° C. and then cooled to roomtemperature. 8.13 g of P₂O₅ was added to the mixture to bring thepolymer concentration to 14%. The mixture was heated at 160° C. for 16hours. As the temperature increased, stir opalescence began to occur atabout 155° C. The mixture was finally heated to 190° C. and held for anadditional 4 hours.

No graphene nanoparticles aggregates were observed in opticalmicrographs taken of the 2,5-Di-OH PBO/GS dope under cross polarizers,indicating good nanosheets dispersion at the optical scale during2,5-Di-OH PBO polymerization. An aliquot of the polymer dope wasprecipitated in water, broken up with a blender, collected by suctionfiltration, washed with water and dried under reduced pressure (0.02mmHg) at 100° C. for 24 hours. An intrinsic viscosity of 17 dl/g wasdetermined in methanesulfonic acid, at 30° C.

Example V

PBO/GS(80/20)

A composition of 2.0% graphene nanoparticles and 80%polyphenylenebenzobisoxazole (PBO) was prepared as follows. Into thebottom of a 250-ml resin flask equipped with a mechanical stirrer, anitrogen inlet and outlet, was placed 4.2612 g (0.02 mol) of1,4-diaminoresorcinol dihydrochloride, 4.0605 g (0.02 mol) ofterephthaloyl chloride, and 16.87 g of phosphoric acid (85%). Theresulting mixture was dehydrochlorinated under nitrogen atmosphere at65° C. for 16 hours. The temperature was then raised to 80° C. and heldfor 4 hours, 0.94 g of graphene nanoparticles (chemical synthesizedgraphene nanoparticles from Angstrom, Inc., Dayton, Ohio) was added tothe mixture. The mixture was heated at 100° C. for 16 hours and thencooled to room temperature. 11.16 g of P₂O₅ was added to the mixture togenerate polyphosphoric acid (77% P₂O₅). The mixture was stirred for 2hours at 80° C. and then cooled to room temperature, 13.4 g of P₂O₅ wasadded to the mixture to bring the polymer concentration to 10%. Themixture was heated at 160° C. for 16 hours. As the temperatureincreased, stir opalescence began to occur at about 155° C. The mixturewas finally heated to 190° C. and held for an additional 4 hours. Analiquot of the polymer dope was precipitated in water, broken up with ablender, collected by suction filtration, washed with water and driedunder reduced pressure (0.02 mmHg) at 100° C. for 24 hours. An intrinsicviscosity of 15 dl/g was determined in methanesulfonic acid, at 30° C.

Example VI

PBO Control

Polyphenylenebenzobisoxazo (PBO) was prepared as follows. Into thebottom of a 250-ml resin flask equipped with a mechanical stirrer, anitrogen inlet and outlet, was placed 4.2612 g (0.02 mol) of1,4-diaminoresorcinol dihydrochloride, 4.0605 g (0.02 mol) ofterephthaloyl chloride, and 16.87 g of phosphoric acid (85%). Theresulting mixture was dehydrochlorinated under nitrogen atmosphere at65° C. for 16 hours. The temperature was then raised to 80° C. held for4 hours. The mixture was then healed 100° C. for 16 hours and thencooled to room temperature. 11.16 g of P₂O₅ was added to generatepolyphosphate acid (77% P₂O₅). The mixture was stirred for 2 hours at80° C. and cooled to room temperature. 13.4 g of P₂O₅ was added to bringthe polymer concentration to 10%. The polymer mixture was heated at 160°for 16 hours. As the temperature increased, stir opalescence began tooccur at about 155° C. The mixture was finally heated to 190° C. andheld for an additional 4 hours. An aliquot of the polymer dope wasprecipitated in water, broken up with a blender, collected by suctionfiltration, washed with water and dried under reduced pressure (0.02mmHg) at 100° C. for 24 hours. An intrinsic viscosity of 22 dl/g wasdetermined in methanesulfonic acid at 30° C.

Example VII

Di-OH PBI/GS (95/5)

A composition of 5% graphene nanoparticles (GS) and 95%2,5-dihydroxy-phenylenebenzobisimidazole (Di-OH-PBI) was prepared asfollows. Into the bottom of a 250-ml resin flask equipped with amechanical stirrer, a nitrogen inlet and outlet, was placed 5.6804 g(0.02 mol) of 2,3,5,6-tetraaminobenzene-terahydrochloride, 4.7004 g(0.02 mol) of 2,5-dihydroxyterephthaloyl chloride, and 11.66 g ofphosphoric acid (85%). The resulting mixture was dehydrochlorinatedunder nitrogen atmosphere at 65° C. for 16 hours. The temperature wasthen raised to 80° C. and held for 4 hours. 0.26 g of graphenenanoparticles (chemical synthesized graphene nanoparticles fromAngstrom, Inc., Dayton, Ohio) was added to the mixture. The mixture washeated at 100° C. for 16 hours and then cooled to room temperature. 7.71g of P₂O₅ was added to the mixture to generate polyphosphate acid (77%P₂O₅). The mixture was stirred for 2 hours at 80° C. and then cooled toroom temperature. 12.14 g of P₂O₅ was added to the mixture to bring thepolymer concentration to 14%. The mixture was heated at 165° C. for 16hours. As the temperature increased, stir opalescence began to occur atabout 158° C. The mixture was finally heated to 190° C. and held for anadditional 4 hours. An aliquot of the polymer dope was precipitated inwater, broken up with a blender, collected by suction filtration, washedwith water and dried under reduced pressure (0.02 mmHg) at 100° C. for24 hours. An intrinsic viscosity of 18 dl/g was determined inmethanesulfonic acid at 30° C.

Example VIII

Di-OHPPBI/GS (95/5)

A composition of 5% graphene nanoparticles and 95%polydihydroxyphenylenepyridobisimidazole (Di-OHPPBI) was prepared asfollows. Into the bottom of a 250-ml resin flask equipped with amechanical stirrer and a nitrogen inlet/outlet was placed 5.3310 g (0.02mol) of 2,3,5,6-tetraaminopyridine-trihydrochloride-monohydrate, 4.7004g (0.02 mol) of 2,5-dihydroxyterephthaloyl chloride, and 11.66 g ofphosphoric acid (85%). The resulting mixture was dehydrochlorinatedunder nitrogen atmosphere at 65° C. for 16 hours. The temperature wasthen raised to 80° C. and held for 4 hours, 0.26 g of purified graphenenanoparticles (chemical synthesized graphene nanoparticles fromAngstrom, Inc., Dayton, Ohio) was added to the mixture. The mixture washeated at 100° C. for 16 hours and then cooled to room temperature. 7.71g of P₂O₅ was added to the mixture to generate polyphosphoric acid (77%P₂O₅). The mixture was then stirred for 2 hours at 80° C. and cooled toroom temperature. 12.14 g of P₂O₅ was added to the mixture to bring thepolymer concentration to 14%. The mixture was then heated at 165° C. for16 hours. As the temperature increased, stir opalescence began to occurat about 158° C. The mixture was finally heated to 190° C. and held foran additional 4 hours. An aliquot of the polymer dope was precipitatedin water, broken up with a blender, collected by suction filtration,washed with water and dried under reduced pressure (0.02 mmHg) at 100°C. for 24 hours. An intrinsic viscosity of 19.0 dl/g was determined inmethanesulfonic acid at 30° C.

Example IX

Di-OHPBI/GS (80/20)

A composition of 20% graphene nanoparticles (GS) and 80%2,5-dihydroxy-phenylenebenzobisimidazole (Di-OH-PBI) was prepared asfollows. Into the bottom of a 250-ml resin flask equipped withmechanical stirrer, a nitrogen inlet and outlet, was placed 5.6804 g(0.02 mol) of 2,3,5,6-tetraaminopyridine-trihydrochloride-monohydrate,4.7004 g (0.02 mol) of 2,5-dihydroxyterephthaloyl chloride, and 11.66 gof phosphoric acid (85%). The resulting mixture was dehydrochlorinatedunder nitrogen atmosphere at 65° C. for 16 hours. The temperature wasthen raised to 80° C. and held for 4 hours, 1.04 g of graphenenanoparticles (chemical synthesized graphene nanoparticles fromAngstrom, Inc., Dayton, Ohio) was added to the mixture. The mixture washeated at 100° C. for 16 hours and then cooled to room temperature. 7.71g of P₂O₅ was added to the mixture to generate polyphosphoric acid (77%P₂O₅). The mixture was stirred for 2 hours at 80° C. and then cooled toroom temperature. 12.14 g of P₂O₅ was added to the mixture to bring thepolymer concentration to 14%. The mixture was heated at 165° C. for 16hours. As the temperature increased, stir opalescence began to occur atabout 158° C. The mixture was finally heated to 190° C. and held for anadditional 4 hours. An aliquot of the polymer dope was precipitated inwater, broken up with a blender, collected by suction filtration, washedwith water and dried under reduced pressure (0.02 mmHg) at 100° C. for24 hours. An intrinsic viscosity of 15.5 dl/g was determined inmethanesulfonic acid at 30° C.

Example X

BBL Control

A ladder polymer, benzimidazobenzophenanthroline (BBL) was prepared asfollows. Into the bottom of a 250-ml resin flask equipped with amechanical stirrer, a nitrogen inlet and outlet, was placed 5.6804 g(0.02 mol) of 1,2,4,5-tetraaminobenzene tetrahydrochloride, 6.0842 g(0.02 mol) of 1,4,5,8-naphthalenetetracarboxylic acid, and 16.16 g ofphosphoric acid (85%). The resulting mixture was dehydrochlorinatedunder nitrogen atmosphere at 65° C. for 16 hours. The temperature wasthen raised to 80° C. and held for 4 hours. The mixture was heated at100° C. for 16 hours and then cooled to room temperature. 10.69 g ofP₂O₅ was added to the mixture to generate polyphosphoric acid (77%P₂O₅). The mixture was stirred for 2 hours at 80° C. and cooled to roomtemperature. 20.02 g of P₂O₅ was added to the mixture to bring thepolymer concentration to 12%. The mixture was then heated at 160° C. for16 hours. As the temperature increased, stir opalescence began to occurat about 160° C. The mixture was finally heated to 190° C. and held foradditional 4 hours. An aliquot of the polymer dope was precipitated inwater, broken up with a blender, collected by suction titration, washedwith water and dried under reduced pressure (0.02 mmHg) at 100° C. for24 hours. An intrinsic viscosity of 23.0 dl/g was determined inmethanesulfonic acid at 30° C.

Example XI

ABPBI-PBO-ABPBI/GS (90/10)

Poly(2,5-benzimidazole)-block-poly(2,5-dihydroxy-1,4-phenylenebenzobisthiazole)-block-poly(2,5-benzimidazole)(ABPBI-DiOHPBO-ABPBI) was prepared as follows. Into the bottom of a250-ml resin flask equipped with a mechanical stirrer, a nitrogen inletand outlet, was placed 4.2612 g (0.02 mol) of 1,4-diaminoresorcinoldihydrochloride, 4.0605 g (0.021 mol) of terephthaloyl chloride, and16.87 g of phosphoric acid (86%). The resulting mixture wasdehydrochlorinated under nitrogen atmosphere at 65° C. for 16 hours. Thetemperature was then raised to 80° C. and held for 4 hours, 0.46 g ofpurified graphene nanoparticles (chemical synthesized graphenenanoparticles from Angstrom, Inc., Dayton, Ohio) was added to themixture. The mixture was then heated at 100° C. for 16 hours and thencooled to room temperature. 11.16 g of P₂O₅ was added to generatepolyphosphate acid (77% P₂O₅). The mixture was stirred for 2 hours at80° C. and cooled to room temperature. 13.4 g of P₂O₅ was added to bringthe polymer concentration to 10%. The polymer mixture was heated at 160°C. for 5 hours. As the temperature increased, stir opalescence began tooccur at about 155° C. The viscous solution was cooled to 65° C. and0.52 g (0.0027 mol) of 3,4-diaminobenzoic acid monohydrochloride wasadded. The resulting mixture is heated slowly under inert gas atmosphereto about 100° C. for a period of about 6 hours to effect thedehydrochlorination. Following the dehydrochlorination, the reaction wasslowly heated back to 165° C. and maintained at that temperature for 10to 12 hours. The mixture was finally heated to 190° C. and held for anadditional 4 hours. An aliquot of the polymer dope was precipitated inwater, broken up with a blender, collected by suction filtration, washedwith water and dried under reduced pressure (0.02 mmHg) at 100° C. for24 hours. An intrinsic viscosity of 16 dl/g was determined inmethanesulfonic acid at 30° C.

Example XII

ABPBI-PBO-ABPBI Control

Poly(2,5-benzimidazole)-block-poly(2,5-dihydroxy-1,4-phenylenebenzobisthiazole)-block-poly(2,5-benzimidazole)(ABPBI-DiOHPBO-ABPBI) was prepared as follows. Into the bottom of a250-ml resin flask equipped with a mechanical stirrer, a nitrogen inletand outlet, was placed 4.2612 g (0.02 mol) of 1,4-diaminoresorcinoldihydrochloride, 4.0605 g (0.021 mol) of terephthaloyl chloride, and16.87 g of phosphoric acid (85%). The resulting mixture wasdehydrochlorinated under nitrogen atmosphere at 65° C. for 16 hours. Thetemperature was then raised to 80° C. and held for 4 hours. The mixturewas then heated at 100° C. for 16 hours and then cooled to roomtemperature. 11.16 g of P₂O₅ was added to generate polyphosphoric acid(77% P₂O₅). The mixture was stirred for 2 hours at 80° C. and cooled toroom temperature. 13.4 g of P₂O₅ was added to bring the polymerconcentration to 10%. The polymer mixture was heated at 160° C. for 5hours. As the temperature increased, stir opalescence began to occur atabout 155° C. The viscous solution was cooled to 65° C. and 0.52 g(0.0027 mol) of 3,4-diaminobenzoic acid monohydrochloride was added. Theresulting mixture is heated slowly under inert gas atmosphere to about100° C. for a period of about 6 hours to effect the dehydrochlorination.Following the dehydrochlorination, the reaction was slowly heated backto 165° C. and maintained at that temperature for 10 to 12 hours. Themixture was finally heated to 190° C. and held for an additional 4hours. An aliquot of the polymer dope was precipitated in water, brokenup with a blender, collected by suction filtration, washed with waterand dried under reduced pressure (0.02 mmHg) at 100° C. for 24 hours. Anintrinsic viscosity of 20.5 dl/g was determined in methanesulfonic acidat 30° C.

Example XIII

Preparation of BBL/GS Composite Film (50/50)

To prepare the nanocomposites, 0.5 g of graphene was first dispersed in20 ml of methane sulfonic acid by stirring for 24 hours. 0.5 g of ladderpolymer, BBL prepared according to the procedure X was added to themixture and stirred for another 24 hours. The resulting mixture wasslowly precipitated into 1 L of stirring methanol. The compositesuspension in methanol was filtered through a 600 mL fine frittedfunnel. A freestanding, aggregated film was formed on the surface of thefunnel and was washed extensively until free of residue acid. The filmwas removed after air-dried for 24 hours and vacuum-dried for severaldays in the 100-130° C. range.

Example XIV

BBL/GS (80/20) Fiber Formation

Fibers of the polymer composition of 20% graphene nanoparticles (GS) and80% BBL as made by the procedure in Example I, were dry-jet wet spunusing a piston driven spinning system manufactured by BradfordUniversity Research Ltd. The polymer dope was first preheated to 50° C.for about 15 minutes. The polymer dope was then formed into acylindrical shape under dry nitrogen and transferred to the spinningcylinder. The polymer composition was heated at 100° C. for about fivehours before spinning. A 50-.mu.m stainless steel filter (from AndersonWire Works, Inc.) filter was used in-line for fiber spinning and thespinneret diameter was 250 .mu.m. A 30-mm spinning cylinder was usedwith a 28-mm diameter piston. The length of the air gap was 10 cm andlength of the coagulation bath was 75 cm. Spun fiber was washed inwater, dilute ammonia, then water for one week, vacuum dried at 80° C.for 12 hours and subsequently heat-treated in a Thermolyne 21100 tubefurnace at 400° C. in nitrogen under tension for 2 minutes.

Example XV

ABPBI-PBO-ABPI/GS(90/10) Fiber Formation

Fiber formation with the polymer composition of 10% graphenenanoparticles (GS) and 90% ABPBI-PBO-ABPBI, as made by the procedure inExample XI, was dry-jet wet spinning with a piston driven spinningsystem manufactured by Bradford University Research Ltd. The polymerdope was then formed into a cylindrical shape under dry nitrogen andtransferred to the spinning cylinder. The polymer composition was heatedat 100° C. for about five hours before spinning. A 50-.mu.m stainlesssteel filter (from Anderson Wire Works, Inc.) fitter was used in-linefor fiber spinning and the spinneret diameter was 250 .mu.m, A 30-mmspinning cylinder was used with a 28-mm diameter piston. The length ofthe air gap was 10 cm and length of the coagulation bath was 75 cm. Spunfiber was washed in water, dilute ammonia, then water for one week,vacuum dried at 80° C. for 12 hours and subsequently heat-treated in aThermolyne 21100 tube furnace at 400° C. in nitrogen under tension for 2minutes.

Example XIV

ABPBI-PBO-PBI Control Fiber Formation

Fibers ofpoly(2,5-benzimidazole)-block-poly(2,5-dihydroxy-1,4-phenylenebenzobisthiazole)-block-poly(2,5-benzimidazole)(ABPBI-DiOHPBO-ABPBI), as made by the procedure in Example XII, weredry-jet wet spun using a piston driven spinning system manufactured byBradford University Research Ltd. The polymer dope was first preheatedto 50° C. for about 15 minutes. The polymer dope was then formed into acylindrical shape under dry nitrogen and transferred to the spinningcylinder. The polymer was heated at 100° C. for about five hours beforespinning. A 50-.mu.m stainless steel filter (from Anderson Wire Works,Inc.) was used in-line for fiber spanning and the spinneret diameter was250 .mu.m. A 30-mm spinning cylinder was used with a 28-mm diameterpiston. The length of the air gap was 10 cm and length of thecoagulation bath was 75 cm. Spun fiber was washed in water, diluteammonia, and water for one week, vacuum dried at 80° C. for 12 hours andsubsequently heat-treated in a Thermolyne 21100 tube furnace at 400° C.in nitrogen under tension for 2 minutes.

Example XV

Fiber Testing

Tensile modulus, tensile strength, and elongation to break weredetermined for the BBL-based fibers prepared according to Examples XIand BBL/GS (80/20) according to example XII, respectively. The fiberswere mounted on cardboard tabs. Tensile testing was performed on anInstron Universal Tensile Tester (Model 5567) at 2.54 cm gauge length ata strain rate of 2% per minute. Fiber diameters were measured usinglaser diffraction. About 20 samples of each fiber were tested. The dataare given in Table 1.

TABLE 1 Mechanical Properties of BBL and BBL/GS (80/20) compositefibers. Intrinsic Fibers viscosity Graphene Strength Elongation Modulus(as spun) (dL/g) (wt %) (GPa) (%) (GPa) BBL 22.8 0 0.83 2.50 70.6polymer BBL/Graphene 17.0 20 1.92 6.15 42.3

Example XVI

Film Testing—Tensile Modulus, Strength, Elongation

Tensile modulus, tensile strength, and elongation to break weredetermined for the BBL/GS (80/20), BBL/GS (70/30); and BBL/GS (50/50),and BBL control films, respectively. The films were mounted on cardboardtabs. Tensile testing was performed on an Instron Universal TensileTester (Model 5567) at 2.54 cm gauge length at a strain rate of 2% perminute. Films diameters were measured using laser diffraction. About 20samples of each fiber were tested. The data are given in Table 2.

TABLE 2 Mechanical Properties of BBL, BBL/GS (80/20), BBL/GS (70/30),and BBL/GS (50/50) films. BBL/Graphene Sample BBL 80/20 70/30 50/50Tensile Average 20.6 51.4 72.4 31.4 Strength Max 24.0 63.0 87.9 32.3(Mpa) Tensile Average .97 2.05 1.31 1.33 Modulus Max 1.20 2.06 1.81 2.09(Gpa) Tensile Average 6.7 13.0 9.2 8.0 Elongation Max 8.7 16.2 11.1 9.65(%)

The data show that the tensile strength as well as elongation to breakof BBL/GS (80/20) fibers are higher than comparable measurements of thecontrol BBL by about 231 and 246%, respectively. The data show thattensile modulus, tensile strength, as well as elongation to break ofBBL/GS (80/20) films are ah higher than comparable measurements for thecontrol BBL fibers by about 249, 211 and 194%, respectively. The averagetensile strength values for the BBL control films varied between 1.8 and2.6 GPa, while the average tensile strength values for the BBL/GS(80/20) films varied between 2.9 and 4.2. Thus, for various trials, atensile strength increase of 40 to 60% was obtained by incorporating 20wt % GS in BBL. The stress-strain curves for BBL/GS (80/20) and BBLcontrol fibers are shown in FIG. 1. Thermal degradation for BBL/GSfiber, conducted at 10° C./min using a TA instruments TGA 2950, showthat the onset temperature of degradation as high as 600° C. and 700° C.in air and in nitrogen atmosphere, respectively, as shown in FIG. 4.

Example XVII

Film Testing—Dispersion

Dispersion of graphene nanoparticles in the polymer composite wasdetermined for BBL/GS (80/20), BBL/GS (70/30), and BBL/GS (50/50), andBBL control cast nanocomposite films by x-ray diffraction. The x-raydiffraction data, shown in FIG. 2, demonstrate a 2θ peak at 26.65°,corresponding to interatomic spacing between two graphene monolayers(d-spacing or degree spacing) of 3.35 angstroms. This data illustratesthat the stacked graphene monolayers with a 3.35 degree spacing betweenthem have the same degree spacing as graphite (comprising 100 or morelayers of graphene).

The number of graphene monolayers in a nanoparticle at the weightloadings indicated above were estimated using the Sherrer formula(D_(p)=(Kλ)/β_(1/2) cos θ)), where the Sherrer factor (K) for plateletmorphologies is 0.94, the excitation wavelength (λ) is 1.5418 angstroms,the width at half the maximum intensity (β_(1/2)) is 0.0112 radians (for50 wt % loadings), and the peak position of 2θ is 26.65°. The averagecrystallite size was determined to be 13.29 nm. Using 3.35 nm as thespacing between layers, nanoparticulates at 50 wt % loading weredetermined to be comprised of approximately 39 layers of graphene. Asseen in FIG. 2, 2θ peaks remain approximately constant for grapheneloadings of 20 wt %, 30 wt %, and 50 wt %, illustrating no furtheragglomeration of graphene with increased loadings and constant degree ofdispersion.

FIGS. 5 and 8 show TEM and SEM micrographs, respectively, of a graphenenanoparticle comprising BBL/GS (50/50). These figures provide opticalconfirmation of the approximate thickness of the nanoparticle structureand average composition of 5-10 graphene monolayers.

All of the compositions and methods disclosed and claimed herein can bemade and executed without undue experimentation in light, of the presentdisclosure. While the compositions and methods of this invention havebeen described in terms of preferred embodiments, it will be apparent tothose of skill in the art that variations may be applied to thecompositions and methods and in the steps or in the sequence of steps ofthe method described herein without departing from the concept, spiritand scope of the invention. More specifically, it will be apparent thatcertain agents which are both chemically and physiologically related maybe substituted for the agents described herein while the same or similarresults would be achieved. All such similar substitutes andmodifications apparent to those skilled in the art are deemed to bewithin the spirit scope and concept of the invention as defined by theappended claims.

What is claimed is:
 1. A method for preparing a polymer composite comprising a polymer and graphene nanoparticles dispersed in the polymer, the process comprising forming a reaction mixture comprising rigid-rod monomers and oligomers containing repeal units derived from the rigid-rod monomer, the oligomers having, on average, about 5-10 repeat units, adding graphene nanoparticles to the reaction mixture, and polymerizing the reaction mixture to form a polymer composite comprising a polymer and graphene nanoparticles dispersed in the polymer, the polymer comprising at least 50 wt % rigid rod polymer repeat units, wherein the graphene nanoparticles, on average, contain less than 25 planar graphene sheets in a stacked arrangement, and wherein the rigid rod polymer repeat units are derived from repeat units corresponding to Formula 1 or Formula 2

wherein the A¹ ring is a six-membered aromatic or a six-membered heterocyclic ring, Y is —O—, —S— or —NR′, R′ is hydrogen, hydrocarbyl, substituted hydrocarbyl or acyl, and X₁ and X₂ are independently a bond, para-ordered aryl or para-ordered heterocyclic ring.
 2. The method of claim 1 wherein the A¹ ring is selected from the group consisting of


3. The method of claim 1 wherein at least 50 wt % of the polymer is derived from repeat units corresponding to Formula 1A, 1B, 1C, 1D, 2A, 2B, 2C or 2D

wherein Y, X₁ and X₂ are as defined in claim
 1. 4. The method of claim 1 wherein X₁ and X₂ are each a bond.
 5. The method of claim 1 wherein X₁ is a bond and X₂ corresponds to Formula 3

wherein n is 0-4, each R₂ is independently hydrogen, hydrocarbyl, substituted hydrocarbyl, hydroxy, halo, phospho (—PO₃H), or sulfo (—SO₃H), and “*” designates the point of attachment of the A² ring system to the remainder of the repeat unit.
 6. The method of claim 1 wherein X₁ is a bond and X₂ corresponds to Formula 3A, 3B or 3C

wherein n is 0-4, each R₂ is independently hydrogen, hydrocarbyl, substituted hydrocarbyl, hydroxy, halo, phospho (—PO₃H), or sulfo (—SO₃H), and “*” designates the point of attachment of the A² ring system to the remainder of the repeat unit.
 7. The method of claim 3 wherein X₁ and X₂ independently correspond to Formula 3

wherein n is 0-4, each R₂ is independently hydrogen, hydrocarbyl, substituted hydrocarbyl, hydroxy, halo, phospho (—PO₃H), or sulfo (—SO₃H), and “*” designates the point of attachment of the A² ring system to the remainder of the repeat unit.
 8. The method of claim 3 wherein X₁ is a bond and X₂ corresponds to Formula 3A, 3B or 3C

wherein n is 0-4, each R₂ is independently hydrogen, hydrocarbyl, substituted hydrocarbyl, hydroxy, halo, phospho (—PO₃H), or sulfo (—SO₃H), and “*” designates the point of attachment of the A² ring system to the remainder of the repeat unit.
 9. The method of claim 1 wherein at least 50 wt % of the polymer is derived from repeat units corresponding to Formula 1I, 1J, 1K, 1L, 2I, 2J, 2K or 2L

wherein Y, R′, X₁ and X₂ are as defined in claim
 1. 10. The method of claim 1 wherein at least 50 wt % of the polymer is derived from rigid rod ladder polymer repeat units corresponding to Formula 6


11. The method of claim 1 wherein the graphene nanoparticles are present at a concentration in the range of about 5 wt % to about 50 wt % of the polymer composite.
 12. The method of claim 11 wherein the graphene nanoparticles are present at a concentration in the range of about 10 wt % to about 50 wt % of the polymer composite.
 13. The method of claim 1 wherein the graphene nanoparticles contain, on average, less than 10 graphene sheets in a stacked arrangement.
 14. The method of claim 1 wherein the tensile strength of the polymer composite is at least 50% greater than the tensile strength of the base polymer of the polymer composite.
 15. The method of claim 1 wherein the tensile strength of the polymer composite is at least 100% greater than the elongation-to-break property of the base polymer of the polymer composite.
 16. The method of claim 1 wherein the graphene nanoparticles are present at a concentration in the range of about 10 wt % to about 50 wt % of the polymer composite and at least 70 wt % of the polymer is derived from rigid rod polymer repeat units.
 17. The method of claim 1 wherein the rigid rod polymer contains repeat units selected from the group comprising benzobisazole, pridobisimidazole, and benzamidazobenzo-phenanthroline.
 18. The method of claim 1 further comprising spinning the polymer composite into a fiber.
 19. The method of claim 18 wherein the fiber is spun by a dry-jet wet technique.
 20. The method of claim 18 further comprising washing and drying the fiber. 